1. Field of the Invention
The present invention relates to a signal processing apparatus for processing an image signal, such as a switcher, a DVE, or a device for recording or reproducing an image signal, for instance, a device for processing, recording, reproducing and transmitting an image signal which is applicable to a digital VTR.
2. Description of the Prior Art
In recent years, new broadcasting systems such as an EDTV 2 system or an HDTV system have been developed and the broadcasting has been started. However, in the EDTV 2 system, although private or exclusive cameras or VTRs thereof have been already commercialized, exclusive or private switchers or editing devices have not been yet brought to market.
Initially, the EDTV 2 system will be briefly explained hereinbelow.
The EDTV 2 system is based on progressive scanning signals (refereed to as progressive signals, hereinafter) which are different from interlace scanning signals (referred to as interlace signals, hereinafter) of a current system. FIG. 15 is a schematic view of the interlace signals and the progressive signals.
Referring to FIG. 15, the interlace signal system is constituted of 30 image data for one second and one image has 525 scanning lines. The scanning lines of one image data including the 525 scanning lines are interlace-scanned one by one. Thus, in the interlace system, the 30 image data is transmitted by 262.5 scanning lines so that it is transmitted as 60 image data for one second.
On the other hand, the progressive signal system is constituted of 60 image data for one second. One of the 60 image data comprises 525 scanning lines which are not interlace scanned.
The progressive signal composed of the 525 scanning lines per image 1 plane is digitized in the form of 8:4:4 of a sampling frequency two times as high as that of what is called a 4:2:2 signal which is specified by a Recommendation ITU-R. 601-3. The sampling frequency is two times as high as that of the 4:2:2 signal and a luminance signal has a frequency of 27 MHZ and a color difference signal has a frequency of 13.5 MHZ.
There has been developed a method in which such 8:4:4 signals are alternately divided every line into a main signal comprising one luminance signal and two color difference signals and a sub-signal comprising one luminance signal and two color difference signals so as to interpolate the main signal and they are transmitted. In the above mentioned method, the main signal and the sub-signal are not only interlace signals each having 525 scanning lines for one frame but also 4:2:2 signals. The above described main signal is added to the sub-signal and they are called a 4:2:2:4:2:2 signal.
For transmitting the above mentioned 8:4:4 signal or the 4:2:2:4:2:2 signals, there has been proposed a method that, for example, a vertical filter 49 as illustrated in FIG. 16 is vertically applied to the color difference signals of the 8:4:4 signal to control a band, by employing the visual characteristic of human beings who do not feel that the color difference signals having the quantity of information lower than those of the luminance signals are extremely deteriorated, and then, the color difference signal is transmitted for every line. In FIG. 16, numeric characters designate coefficients of a multiplier. Thus, the above mentioned 4:2:2:4:2:2 signal is transmitted as a 4:2:2:4:0:0 signal having the sub-signal including no color difference signal. The 4:2:2:4:0:0 signal is called a 420P signal. The 420P signal transmitting system has been disclosed as an SMPTE 294M standard. When the progressive signals are transmitted or recorded and reproduced, if the progressive signals are converted into the above described 420P signals, and the 420P signals are transmitted, or recorded and reproduced, the transmission band of the signals can be effectively reduced without visually deteriorating the image signals.
In the case of the 420P signals, image signals are divided into main signals and sub-signals respectively in a frame n and a frame (n+1), as can be seen in FIG. 17. The main signals and the sub-signals are arranged in the form of a grid in the frame n and the frame (n+1) in terms of time space or interval. Then, the color difference signals which are subjected to a band control by for instance, the vertical filter 49 shown in FIG. 16, are decimated for every one line, so that only the color difference signals in the main signal sides are transmitted and the color difference signals in the sub-signal sides are not transmitted. The color difference signals in the sub-signal sides which are decimated in such a way can be reproduced by, for example, applying an interpolating filter 50 to the main signals, as shown in FIG. 18.
A recording and reproducing device or an editing device to which the above mentioned 420P signals can be directly inputted have not been yet brought to market. In a conventional recording and reproducing device, two 4:2:2 signals, in other word, what is called a 4:2:2:4:2:2 signal, have been inputted thereto, color difference signals thereof have been decimated by the vertical filter 49 (see FIG. 16), the obtained signals have been recorded and reproduced as a 420P signal and the color difference signals of a sub-signal side in the reproduced 420P signal have been subjected to an interpolating processing in the interpolating filter 50 (see FIG. 18), so that the obtained signals have been outputted as two 4:2:2 signals.
Further, in a conventional editing device, progressive scanning signals have been treated as two interlace signals, so that operations such as an editing operation, a synthesizing operation and so on have been carried out.
As a conventional recording and reproducing device for 420P signals, for example, a VTR, has been put to practical use, in which a signal processing adapter is combined with what is called a D5VTR disclosed in a PROPOSED SMPTE STANDARD for Digital Video Recording 1/2-in Type D-5 Component Format 525/60 and 625/50 (SMPTE 279M, SMPTE, Journal, May 1995). According to the above described 3 conventional recording and reproducing device, that is, the VTR, the 420P signals have been highly efficiently decoded so as to further reduce a signal band and the signals have been recorded on the D5VTR capable of recording and reproducing the present 4:2:2 signals.
Now, an explanation will be given to a conventional system or method for a signal processing.
FIG. 19 is a block diagram showing an example of a signal processing part of the D5VTR system for recording and reproducing, for instance, the TV signals of an EDTV 2 system.
In FIG. 19, progressive scanned EDTV 2 signals are inputted. An input signal 51 is composed of two interlace signals. Color difference signals in a sub-signal side are decimated by a color signal decimating means 52. A recording signal processing means 53 carries out a highly efficient decoding processing for images and an interleaving processing for preventing the error propagation of images by using a first storing means 54. At this time, the delay of one field is generated in the processing for interleaving two fields into those of the highly efficiently decoded signals of the images. A recording signal 55 outputted from the recording signal processing means 53 is recorded on a recording medium 56. A field termed herein means the field of the interlace signal and has a frequency of 60 Hz.
A reproduced signal 57 reproduced from the recording medium 56 is inputted to a reproduced signal processing means 58. In the reproduced signal processing means 58, an error correcting processing, a deinterleaving processing and a highly efficient decoding processing are conducted by using a second storing means 59. In the reproduced signal processing means 58, the delay of two fields is generated in the deinterleaving processing. Further, the delay of two fields is generated also in the highly efficiently decoding processing. A delay time necessary for the deinterleaving processing may be one field at a minimum. However, usually, two fields are required for the delay time to provide a surplus in a slow processing or the like. Then, the color difference signals in the sub-signal side of the 420P signal are interpolated by a color difference signal interpolating means 60 so that the signal is outputted as two 4:2:2 signals 61.
However, according to the conventional signal processing method, all the delay time required for the signal recording processing and the signal reproducing processing reaches a frame expressed by odd numbers. The 420P signal has a construction as illustrated in FIG. 17. The sampling position of the main signal is different from that of the sub-signal between a frame n and a frame (n+1). Therefore, when the total of delay time reaches time indicated by the frame expressed by odd numbers, the sub-signals are outputted to the sampling positions of the main signals located in the frame represented by even numbers and the main signals are outputted to the sampling positions of the sub-signals in order to maintain the frame structure of images.
In addition, also in the frame of odd numbers, the sub-signals are outputted to the sampling positions of the main signals, and the main signals are outputted to the sampling positions of the sub-signals. As a result, the color difference signals in the sub-signal sides are formed in accordance with an interpolating processing from the main signals. Thus, when a whole delay time becomes time located in the frame expressed by odd numbers, the main signals are undesirably replaced by the sub-signals, so that the color difference signals in the sub-signal sides formed under the interpolating processing are disadvantageously outputted as the main signals.
When the above described signal processing is repeated, the color difference signals synthesized or composed by the interpolating processing are repeatedly subjected to a decimating processing and an interpolating processing. Thus, there has arisen a problem that the qualities of images of the color difference signals are degraded. Specifically stated, both the vertical filter 49 for a decimating processing and the interpolating filter 50 for an interpolating processing cannot realize an ideal filter because of the restriction in the number of taps. If a filtering processing is repeated, the qualities of images of the color difference signals will be undesirably lowered.
When an actual studio system is taken into consideration, the system in which VTRS, switchers and so on are connected in series and in a multiple stage is employed. Therefore, since the color difference signals of an image signal passing through the equipments and devices in a multiple stage with whole delay times located in the frames expressed by odd numbers are repeatedly decimated and interpolated, the qualities of images of the color difference signals have been inconveniently obviously degraded.